This particular invention relates generally to photographic film processing and, more particularly, it concerns a method and photographic film cassette having an improved pressure pad and cooperating fluid processing applicator nozzle for reducing frictional drag on a strip of traveling film and for better controlling the processing fluid thickness on the film.
Multipurpose film cassettes have been developed in which a strip of photographic film is operated so as to be exposed, processed and projected while being at all times in the cassette. Film cassettes of this type are disclosed in several U.S. patents assigned in common with the present invention.
In film cassettes of this category, a supply of light sensitive photographic film can be selectively exposed in a camera particularly adapted to receive and operate the cassette. To process or develop the exposed film, the cassette is removed from the camera and placed in a player or processing and viewing apparatus capable of activating a cassette contained processor for depositing a desired uniform layer of processing fluid on the film's exposed emulsion surface. During such processing a conventional series of successive, positive transparent images on the exposed film is developed. Following processing in the manner indicated, the player apparatus is operated as a projector. During projection, the film is incrementally advanced, frame-by-frame, past a light source. Accordingly, the series of positive transparent images of the scenes to which the film were exposed are capable of being successively viewed while being projected onto a screen.
Towards the end of achieving the desired fluid thickness on the film strip the cassette contains a spring-biased pressure pad for supporting the film including its longitudinal edge rails between the pad and a fluid processor nozzle structure. As so supported, the film strip is directly sandwiched by and between the pressure pad and the nozzle. In this manner, the film's emulsion surface is urged into a predetermined position against the nozzle, whereby it has a uniform and spaced relation to a doctoring surface of the nozzle for effecting formation of the desired thickness, as well as for minimizing film distortion during fluid application. To facilitate continuous formation of the desired thickness, the doctoring surface, which is positioned downstream of a nozzle opening in the direction of film advancement during processing, is constructed to develop positive hydro-dynamic pressures in the deposited fluid flowing therepast so as to force the strip into engagement with the pressure pad. Hydro-dynamic pressures, however, tend to force the film strip away from the doctoring surface. To resist this tendency, the spring biasing the pressure pad is constructed to maintain the emulsion surface in its predetermined position relative to the doctoring surface despite the hydrodynamic forces.
While the spring biased pressure pad and nozzle are successful for positioning the film strip in the intended manner, several drawbacks arise from their use. These are attributable to the fact that the film including longitudinal edge rails is sandwiched directly between the pressure pad and nozzle. One disadvantage is that the spacing desired to bring about the desired fluid thickness can vary in accordance with the thickness variations of the film's longitudinal edge rails. In this context should the film rails be thicker than intended, the pressure pad will be positioned farther from the doctoring surface. Consequently, spacing between the doctoring surface and image areas of the film's emulsion surface will be increased, thereby undesirably increasing processing fluid thickness. On the other hand, should the film rails be thinner than intended, the pressure pad, owing to its biasing spring, will force the strip closer to the doctoring surface, whereby the pressure pad will cause the latter to be bowed towards the doctoring surface. This has the effect of reducing the gap spacing between the image area on the film's emulsion surface and the doctoring surface and, thereby, reducing the desired fluid thickness. It will be appreciated, therefore, that conventional pressure pad and nozzle arrangements fail to prevent spacing variations between the emulsion layer and the doctoring surface caused by thickness changes of the film, particularly changes in the film's edge rails. Such variations lead to unintended and uneven fluid distribution on the film and thus blemishes in the projected images.
Moreover, the foregoing approach suffers from the fact that relatively high amounts of friction are developed during film strip advancement in either the exposure or processing modes. Increased friction results in increased power requirements during exposure and, thus, shortens useful life of the camera's relatively weak battery power. Also, excessive friction of this type increases film web tension during film strip processing when the cassette is in the player apparatus for processing. Increased tension causes a tight wind on the winding spool, thereby inviting slippage or cinching between adjacent wraps or convolutions of film so that contact between the wraps becomes a problem. Such contact results in processing defects since the freshly deposited processing fluid layer is damaged.
It follows, therefore, that substantial reductions in the drag encountered by a film and the spacing variations of the image area relative to the doctoring nozzle are the focal points of attention to overall system development.
Moreover, the problems of avoiding relatively high frictional drag on the film and irregular coating thickness are further compounded by the requirement the cassette and its components including the pressure pad and fluid processor nozzle structure must be capable of mass production manufacturing techniques as well as be within tolerance levels incident to such techniques for the system to be acceptable in a competitive commercial market. Accordingly, the structional organization of components by which the film is supported in predetermined relationship to the doctoring surface is important to the overall system.